1. Field of the Invention
This invention relates to a photoelectric detection switch for detecting the presence or absence of an object.
2. Description of the Related Art
Hitherto, detection switches such as a photoelectric switches, proximity switches, and ultrasonic switches have been used for detecting the presence or absence of an object moving on a production line in a factory, etc. The detection switch detects the presence or absence of an object by emitting light energy, a magnetic force, an ultrasonic wave, etc., to a sense area and detecting energy reflected from the sense area or energy penetrating the sense area.
For example, the photoelectric switch determines whether or not an object exists by emitting light to the object transport passage and detecting the presence or absence of light reflected from the object or light penetrating the object.
With the photoelectric switch of the penetration type, if the object to be detected does not exist in the sense area, light emitted from a light emission section enters a light reception section. In this case, if the light reception amount level in the light reception section is equal to or less than a predetermined threshold value, the object to be detected is determined to exist. On the other hand, with the photoelectric switch of the reflection type, if the object to be detected exists in the sense area, light emitted from a light emission section is reflected by the object and the reflected light enters a light reception section. In this case, if the light reception amount level in the light reception section exceeds a predetermined threshold value, the object to be detected is determined to exist. The sensitivity of the photoelectric switch is adjusted by changing the threshold value.
With such photoelectric switches, the light reception amount level may lower due to a shift in the optical axis, dirt on the light emission or reception face, characteristic degradation of the light emitting element of the light emission section, etc. Then, if a photoelectric switch has a display section for visually displaying the light reception amount, such lowering of the light reception amount level can be recognized visually. The threshold value of the photoelectric switch can then be changed at the proper time for resetting the sensitivity of the photoelectric switch.
With the photoelectric switch, when the change amount of the light reception amount per unit of time is small, for example, in such a case where the object to be detected does not move as at the installation stage of the photoelectric switch or moves at a very low speed, the light reception amount displayed on the display section can be read, whereby the operator can check whether or not the sensitivity of the photoelectric switch is adequate.
However, when the change amount of the light reception amount per unit of time is large, for example, in such a case where the object to be detected moves at a high speed, the light reception amount displayed on the display section is changed at a high speed, thus it becomes difficult to read the light reception amount. As a result, the operator cannot check whether or not the sensitivity of the photoelectric switch is adequate based on the light reception amount displayed on the display section.
Therefore, to check whether or not the sensitivity of the switch is adequate, measures, such as stopping the production line, need to be taken for lowering the movement speed of the object to be detected. The efficiency of resetting the sensitivity of the switch is very poor.
To detect the object to be detected on the production line, the light reception amount in the photoelectric switch varies due to variations in the position and surface state of each object to be detected. In such a case, the sensitivity of the switch needs to be set so that the detection result is not affected by the variations in the objects to be detected.
It is therefore an object of the invention to provide a detection switch for enabling the setup sensitivity of the switch to be easily checked without lowering the movement speed of an object to be detected.
It is therefore another object of the invention to provide a detection switch for enabling the setup sensitivity of the switch to be easily checked without lowering the movement speed of an object to be detected, and also enabling the sensitivity of the switch to be set so that the detection result is not affected by variations in the objects to be detected.
It is therefore still another object of the invention to provide a photoelectric switch for enabling the setup sensitivity of the switch to be easily checked without lowering the movement speed of an object to be detected.
It is therefore still another object of the invention to provide a photosensitive switch for enabling the setup sensitivity of the switch to be easily checked without lowering the movement speed of an object to be detected and also enabling the sensitivity of the switch to be set so that the detection result is not affected by variations in the objects to be detected.